The IEEE 802. 11e standard formulates a technology for achieving QoS control in a wireless communication system, which is comprised of (i) a communication control apparatus that periodically transmits a control signal and (ii) a communication terminal that performs wireless communication in accordance with the control signal transmitted by the communication control apparatus (see Non-Patent Reference 1). Two access control methods are standardized in the IEEE 802. 11e: an enhanced distributed channel access (EDCA); and a hybrid coordination function controlled channel access (HCCA).
EDCA achieves the QoS control by giving high priority data a good chance of being transmitted. With the EDCA, each of the communication terminals obtains channel access with high probability. In contrast, HCCA achieves the QoS control by allocating a given bandwidth to a specific communication terminal. With the HCCA, a direction of data transmissions is limited to either one of “down-link” (from the communication control apparatus to the communication terminal) or “up-link” (from the communication terminal to the communication control apparatus). By entitling only one specific communication terminal to the channel access, the HCCA can guarantee allocation of the bandwidth to the specific communication terminal.
The communication control apparatus allocates two types of communication periods within a time interval between control signal transmissions, depending on requested bandwidth for transmitting data. One is an HCCA period in which communication is performed with the HCCA, and the other is an EDCA period in which the communication is performed with the EDCA. The communication control apparatus then transmits the control signal, including information indicative of the above allocations. Each of the communication terminals performs the communication in accordance with the above allocations of the HCCA and EDCA that is indicated by the control signal. In this structure, data that requires an adequate amount of bandwidth can be transmitted with the HCCA, so that the data transmission is not affected by other data transmissions. Meantime, data that does not require such a bandwidth can be transmitted with the EDCA.
Non-Patent Reference 1:
IEEE P802.11e/D11.0, “IEEE Standard for Information Technology—Telecommunications and information exchange between systems—Local and metropolitan area networks Specific requirements—Part 11: Wireless Medium Access Control (MAC) and Physical Layer (PHY) specifications: Amendment 7: Medium Access Control (MAC) Quality of Service (QoS) Enhancements”, October 2004